1. Field of the Invention
This invention relates to a mooring system for use in mooring a vessel to a mooring facility on a wharf or a pier.
2. Description of the Prior Art
In case a vessel is moored alongside a quay to a mooring facility on a wharf, it is imperative to arrange a plurality of mooring means in a suitable condition, in consideration of wind pressure, waves or billows, tidal currents coming from every direction, so that a vessel may be moored in a well balanced condition. In general, the mooring means for use to this end of rope securing means such as hook or post are provided on the side of a mooring facility on a wharf, a winch on board the vessel and a plurality of ropes or wires tied down therebetween. In line with an increase in the size of vessels, there have been arisen difficulties in handling those ropes or wires for mooring vessels alongside the quay. More particularly, as vessels are increased in tonnage to as high as several hundred thousands tons, strength required for ropes should necessarily be increased. This leads to an increase in diameter of ropes. However, there are imposed limitations on the diameters of ropes of this kind, from viewpoints of winding and unwinding operations by means of a winch. To cope with this difficulty, there has been proposed an attempt to use a given number of a plurality of ropes as a unit group, so that such groups of ropes are used in the desired mooring conditions. Recently, the number of ropes required has been determined by dividing a maximum design tension strength for one group of ropes by an allowable tension strength for each rope.
However, such an attempt to use a given number of a plurality of ropes a unit group for using such groups of ropes in desired mooring conditions provides only a partial success in this problem. In other words, it was found to be quite difficult that every rope in such groups bears uniform tensional force. In addition, this problem is further plagued with increasing difficulties as the number of ropes is increased. This problem, i.e., adjustment for tension exerted on the respective ropes however has been resorted to a human perception. This apparently leads to the failure in achieving the distribution of uniform tension for the respective ropes. Thus, in the event that tensions higher than a design maximum tension are applied to the ropes, then the ropes are broken in the order of the ropes bearing a higher tension, thus causing accidents.
In addition, there is another type of difficulty in such a mooring system. In the case of unloading of a vessel at its moorings, the vessel is going up above the water surface, as the unloading operation proceeds. As a result, tension exerted on ropes is increased, so that unless the ropes are loosened, then excessive tension is exerted thereon, with the result that excessive force is applied to the contacting portions of a vessel with the quay or the mooring facility on a wharf. This results in breakage either in the fuselage of a vessel or in ropes. Accordingly, ropes should be loosened as the vessel is going up above the water surface, in order to avoid such accidents. Thus it is mandatory to maintain tensional force exerted to ropes in a well balanced condition.